* Detonation/Pre-ignition: The knock sensor's job is to detect detonation (uncontrolled explosions of the air/fuel mixture) in the cylinders. If the sensor is malfunctioning (either failing to detect knock or falsely reporting it), the engine's computer (ECU) won't be able to adjust the ignition timing appropriately. This can lead to continued detonation, which generates excessive heat and pressure.
* Engine damage from detonation: Over time, sustained detonation can cause:
* Damaged pistons: The increased pressure can melt or crack pistons.
* Damaged piston rings: These can become damaged or break, leading to poor compression and oil consumption.
* Damaged cylinder walls: The extreme pressure can also score or damage the cylinder walls.
* Damaged head gasket: The intense heat and pressure can blow a head gasket.
* Rod bearing failure: In severe cases, the extra stress could lead to connecting rod bearing failure.
* Cracked cylinder head: In the worst-case scenario, the cylinder head itself might crack.
* Reduced Engine Performance: Even without catastrophic damage, a bad knock sensor can result in decreased power, rough running, and reduced fuel economy because the engine's timing is not optimized.
In short, a bad knock sensor doesn't directly *cause* major engine damage, but it allows conditions that *lead* to major engine damage if left unaddressed. The damage is often cumulative and can be expensive to repair once it's progressed.
